Numerous designs of passive and active automotive occupant restraint systems are known for enhancing occupant protection in the event of a vehicle impact. Passive systems are deployed with no action required by the occupant and include inflatable restraints or air bags for frontal and side impacts. Automatically deployed seat belt systems are known. Active systems, such as seat belts, have been used for many decades and are manually deployed by the occupant. The conventional seat belt system uses three points of connection with the vehicle structure and incorporates a lap belt portion for engaging the occupant's lower torso, and a shoulder belt portion for engaging the occupant's upper torso. When used, the seat belt restrains movement of the occupant in the event of a vehicle impact or rollover event. In order to enhance the comfort and convenience provided by the seat belt system, retractors are used which permit belt webbing to be extracted from and retracted into the retractor, allowing movement of the occupant while maintaining the belt in close contact with the occupant. An inertia sensitive vehicle sensor which may be used with a webbing sensor, locks the retractor when an impact or rollover event is detected, preventing further extraction of webbing to restrain the occupant.
A more recent development in the area of seat belt systems is that of the so-called inflatable seat belt. An inflatable seat belt system incorporates a section of the shoulder or lap belt section which is inflated by a gas, typically by a pyrotechnic inflator, to increase its size and volume. Thus, when an inflatable seat belt is deployed, the normally narrow seat belt webbing expands significantly to reduce the contact pressure between the belt and the occupant during an impact event. Inflatable seat belts also act as a belt pretensioner by reducing belt slack. In addition, when an inflatable lap belt is deployed, the inflating lap belt may act as a side impact airbag. Inflatable seat belts are typically deployed using the crash sensing systems also used to deploy other inflatable restraint systems upon the detection of a vehicle impact or rollover event having predetermined dynamic characteristics.
Another feature for enhancing performance of seat belt systems is belt pretensioners. Belt pretensioners cinch the seat belt webbing against the occupant, eliminating slack immediately upon the detection of a vehicle impact. Other types act on a seat belt anchorage to pull down on the anchorage to reduce slack. Reducing the slack in the seat belt system enables the occupant's forward motion to quickly engage the seat belt to begin dissipating impact energy. Various designs of retractor pretensioners are presently known, including a type known as a Roto-Pretensioner which incorporates a series of balls in a gas duct which are driven by the firing of a gas generator to engage with and wind the retractor spool sprocket to retract the webbing.
Incorporating seat belt systems such as pretensioners and inflatable set belts increases cost and complexity of the resistant system. Automotive suppliers are under considerable competitive pressure to provide vehicle components which are cost-effective and provide high levels of performance.